Anogenital distances in newborns and children from Spain and Greece: predictors, tracking and reliability.

Background: Anogenital distance has been associated with prenatal exposure to chemicals with anti-androgenic effects. There are limited data in humans concerning descriptive patterns, predictors, and the reliability of measurement of anogenital distances. We examined anogenital distance measurements and their predictors in males and females and further estimated the reliability of these measurements.

Methods: Anogenital distances were measured in repeated time periods among 352 newborns and 732 young children in two cohorts, one in Crete, Greece and one in Barcelona, Spain. Mixed effect models were used to estimate the between-children, between- and within-examiners variance, as well as the reliability coefficients.

Results: Genitalia distances were longer in males than in females. Anogenital distances in both sexes increased rapidly from birth to 12 months, while the additional increase during the second year was small. Birthweight was associated with an increase of 1.9 mm/kg [95% CI 0.1, 3.8] (CI, confidence interval) in the anogenital distance measured from the anus to anterior base of the penis in newborn males, 2.9 mm/kg [95% CI 1.8, 3.9] in anoclitoral distance and 1.0 mm/kg [95% CI 0.0, 2.0] in anofourchettal distance in newborn females, after adjustment for gestational age. In children, body weight was the main predictor of all genitalia measurements. Moreover, anogenital distances at birth were associated with the corresponding distances at early childhood. High reliability coefficients (>90%) were found for all anogenital distances measurements in males and females.

Conclusions: Anogenital distances are strongly related to gestational age and birthweight and later, to growth. They track through early life and are highly reliable measures in both sexes.